The present invention relates in general to semiconductor chips, and more particularly to the formation of electrical contacts on the chips.
The fabrication techniques in forming various digital and analog circuits in semiconductor substrates are well known and documented in the prior art. Irrespective of the type of circuit formed in the semiconductor material, electrical contacts are necessary for accessing the input and output regions of the semiconductor circuits. Much like the fabrication of the circuits in the semiconductor material, the formation of contacts using various metals is also well known. While not an elementary task, the mating of various metals to the silicon or other semiconductor material requires a number of fabrication steps so that the metals can be reliably alloyed to the semiconductor material to provide a low resistance contact.
Many semiconductor devices may be formed in one face or surface of a semiconductor chip. The remainder of the bulk semiconductor material, i.e., the substrate, does not carry signal currents. In this instance, most of the metal contacts are typically formed on the same side, in contact with the various semiconductor regions. In certain cases, the backside of the chip is also metalized to provide a voltage potential thereto for biasing the substrate at a potential with regard to the other voltages applied to the top-side contacts. The backside contact does not otherwise affect the operation of the circuit, nor do signal currents pass through such contact. When fastening the semiconductor chips to metal lead frames, or the like, it can be appreciated that contact need be made only to the top side of the chip, thus construction of the various lead frames is simplified. In other words, if lead frame connections from both top side contacts and bottom side contacts are not required, assembly, packaging and testing of the devices is facilitated.
Other types of semiconductor devices have circuits formed in both face surfaces thereof. In this instance, contacts that carry signal currents are required on both sides. As noted above, this requirement complicates the assembly and testing of the devices. Attempts have been made to provide metal contacts on the same side of the semiconductor chip by way of conductive vias formed through the semiconductor chip from one face to the opposite face thereof. U.S. Pat. No. 3,982,268 by Anthony, et al., discloses a technique for forming active circuits on both sides of a semiconductor chip. These circuits are electrically connected together through the chip by utilizing a via of highly conductive material formed by the thermomigration of a droplet of metal. Electrical contacts are formed on the top and bottom surfaces of the low-resistance via to thereby form a conductive path through the wafer. The circuits on one side are thus connected by way of the via to the circuits on the other side of the chip.
The thermomigration of metal to form the low-resistance region can be accomplished in a relatively short period of time, in that metal diffuses very quickly in semiconductor material in response to a high temperature thermal drive. In U.S. Pat. No. 4,275,410 by Grinberg, et al., micro-interconnects are formed through the semiconductor chip. Aluminum is deposited by a metal evaporator to form aluminum dots on the surface of the chip. The thermomigration process is then carried out to cause the aluminum to diffuse through the chip, from one side to the other. U.S. Pat. No. 5,682,062 by Gaul discloses a method of forming interconnects for stacked integrated circuits. According to this technique, trenches are formed in the semiconductor material, and an insulating silicon oxide is formed on the side wall. Then, a conductive material, such as an N-type doped polysilicon, is deposited so as to fill the trench and form a conductive via from one semiconductor chip surface to the other. While this technique may be effective, numerous processing steps and masks are involved in forming trenches, the deposition of the isolation oxide and refilling the trenches, which all add to the cost of the device.
In accordance with the principles and concepts of the invention, there is disclosed a method for efficiently forming a connector block through a semiconductor chip.
In accordance with one aspect of the invention, active semiconductor regions are formed in the chip to provide a desired electrical function. Formed from one face of the chip to the other is a conductive connector block for carrying current from one face of the semiconductor chip to the other. When the connector block is metalized to form surface contacts, all contacts to the semiconductor device can be formed on one face of the chip.
In another form of the invention, circuits are formed in both faces of the chip. An overvoltage surge device is fabricated so that all terminals thereof are on the same surface of the chip. This facilitates the utilization of a planar lead frame which need only be soldered or bonded to one surface of the chip.
In one application, two overvoltage surge devices employing buried regions are formed in the semiconductor chip, with a highly conductive semiconductor region therebetween functioning as electrical isolation between the devices. At the same time and through the same process step in forming the buried and isolation regions, the connector block is also formed from one face of the semiconductor chip to the other. After metalization, all contacts can be located on the same face of the chip. As many connector blocks can be formed as needed.
In yet another embodiment, the semiconductor chip is formed with at least one active circuit therein. A first contact is formed on one face surface of the chip, in contact with the circuit. A second contact is formed on the same face surface of the chip. A third contact is formed on an opposing side of the semiconductor chip in contact with a circuit. A conductive connector block is formed with nonmetal impurities from one face to the other face surface of the chip, and formed in contact with the second and third contacts. All contacts carrying circuit currents are thus located on one side of the semiconductor chip.
The present invention can provide a conductive path which can be formed through the semiconductor chip from one face surface to the other utilizing standard deposition and semiconductor diffusion techniques with dopants characterized by low diffusion constants. Further, the invention also provides a technique in forming conductive paths through a semiconductor chip by diffusing the impurities therein, together with other impurities to form different semiconductor regions for the active circuits. An advantage of the invention is that conductive paths can by formed by a long term thermal drive of low diffusion constant dopants, at the same time as doped isolation regions are formed. Another advantage of the invention is that it provides a more economical packaging of semiconductor chips by using a single planar lead frame without bending or otherwise soldering plural lead frames together.